1. Field of the Invention
The present invention pertains to an apparatus for detecting an orientation flat of a water and centering the wafer.
2. Prior Art
An orientation flat of a wafer has hitherto been detected by lining and rotating the wafer, sensing the opposite ends of the orientation flat by means of an optical sensor, calculating the angle therebetween based on the amount of rotation in a stepping motor, and correcting the results until a half of the angle is brought into a prescribed position.
Further, the centering of the wafer has been carried out by dropping the wafer into a funnel shaped recess and vibrating it to make the wafer level, or by placing the wafer on a rotating table and sensing the deviation of the outer periphery of the wafer from the center of rotation of the table to compensate the deviation.
Thus, the detection of the orientation flat and the centering of the wafer have hitherto been carred out separately by each exclusive mechanism.
Further, the conventional orientation flat detecting apparatus has the disadvantages that the accuracy in the detection of the opposite ends of the orientation flat is very low. Besides, the apparatus itself is intricate in structure and requires a lot of space for installation. The conventional centering apparatus also has the disadvantages similar to those in the orientation flat detecting apparatus.